Manufacture of steel



atented Feb. 2, 1932 UNITED STATES PATENT OFFICE HANS MEYER, OF HAMBORN, GERMANY, ASSIGNOR TO V'EBEINIGTE STAHLWEBKE AK- TIENGESELLSCHAFT, OF DUSSELDORF, GERMANY, A CORPORATION OF GERMANY MANUFACTURE OF STEEL No Drawing. Application filed November 21, 1927, SerialNo. 234,894, and in Germany December 6, 1927.

The value of ingot steel, such as is used for example for iron constructions, steam boiler making and for reservoirs, as also for various kinds of pipes, is detrimentally in- 6 fluenced by the so called blue fracture or by brittleness due to ageing. If such a steel is cold stressed and then heated to blue heat, that is to about 200 to 300 0., it will become brittle on cooling, that is it ages. If it is 10 however stressed at blue heat, the great brittleness remaining after cooling is called blue brittleness or, when breakage occurs, blue fracture. The two phenomena are similar as regards their nature and only differ quantitatively.

In order to prevent blue fracture and brittleness due to ageing, it has been proposed, to produce a steel by adding further alloy constituents or by special manufacturing 'processes, in which brittleness due to ageing or blue fracture is reduced to a minimum. The only treatment, which has hitherto been applied, in order to prevent brittleness due to ageing and blue fracture, consists in ture in water or oil. By this method the steel becomes very tough and practically free from brittleness due to ageing and from blue fracture. However it again loses this property by a subsequently annealing treatment at a comparatively low temperature.

Applicant has found, that an ingot steel, which without special treatment ages and becomes liable to blue fracture, loses this objectionable property to a very considerable extent, if it is first cold stressed and subsequently heated in suitable manner. to .a temperature between 700 and 950 C. This newly recognized phenomenon is explained afisfollows:

It has already been pointed out, that a cold stretching is accompanied in the steel by a crystallographic direction effect (Werkstoifausschuss of the Verein deutscher Eisenhiittenleute, report 25 by Professor Dr. Korber, of Dusseldorf, Germany). Other experts are, however of the opinion, that the same direction effect exists in those changed parts of the material, which produce blue fracture and lirittleness due to ageing, and which can quenching the material at a high tempera- I be proved by etching the lines of force (Werkstofiausschuss of the Verein deutscher Eisenhiittenleute, report 20 b H. Ma er and W. Eichholz of Hamborn, ermany Experiments have shown, that the detrimental accompanying phenomena of a cold stretching of the steel-hardness and brittlenesscan already be entirely obviated by a heat treatment at about 700 (3., before the crystallographic direction effect caused by the cold 50 stretchin is again lost by the heat treatment. Recently l-I. Tammann and H. H. Meyer of Gottingen, Germany, have found, that with very soft electrolytic iron this or stallographic directiqn effect caused by col drawing or cold rolling, and which can be proved crystallographically or Rontgen spectrographically, is preserved to a certain extent up to annealing temperatures of 1000 C.

and is only completely lost at this temperature (Zeitschrift fur Metallkunde 1926, pages 329 and following).

This invention is based on the following supposition:

If a steel, which by a uniform cold deformation such as drawing or ro1ling, has assumed a directed crystal arrangement throughout, is heated so that it loses its hardness and brittleness, but retains a directed crystal arrangement, it may be assumed, that such a steel can scarcely be altered in an unfavorable manner by a treatment, which would in the ordinary way cause brittleness due to ageing and blue fracture, seeing that the normal result of such an ageing treatment, a directed crystal arrangement in individual steel particles, already exists throughout the Whole of the steel. If however a compulsory' arrangement of the steel articles affected by the ageing. treatment oes not occur, it is to be supposed that a brittleness in the steel particles in question will not arise. Experiments conducted by the applicant have proved this supposition to be correct. Therefore, in order to prevent brittleness due to ageing and blue fracture, it is necessary to heat a previously uniformly cold stretched 'steel in such a manner that, although it loses its brittleness, it retains the directed crystal arrangement. A condition is, that a sufiiciently strong crystallographic direction effect has been imparted to the steel through cold deformation. The heat treatment can be carried out on the lines and temperature limits indicated above between 700 and 950 C., also taking into consideration the degree of cold deformation and the composition of the steel. The length of the annealing period must depend upon the temperature in such a manner, that a higher annealing temperature requires a shorter annealing period.

The circumstances to which the above men- "tioned improvement of the steel is due, result in that a repeated treatment of the steel" by cold stretching and annealing treatment is suitable for increasing the improving efiect. If a single treatment does not attain the desired object, the treatment should consequently be repeated, if necessary with reduclng of the annealing temperature. When choosing the annealing treatment it must be remembered, that temperatures between 700 and 850 C., too long annealing and too slow cooling easily cause a coarsening of the grain by so called recrystallization. This coarsening of the grain must be prevented according to the known laws of recrystallization. In cases, in which a critical degree of cold deformation cannot be prevented, very short annealing at 850 to 900 C. followed by air cooling may consequently be regarded as suitable.

Ewamples 1. A bad boiler plate of the following composition: I

Per cent Carbon 0,145 Manganese 0,51 Phosphorus 0,038 Sulphur 0,062

shows, when delivered, a notching toughness of 13.8 mkgs./cm. and, when aged, still possesses 2-59 mkgs./cm.

The protecting treatment on a testing point consisted in a cold bending followed by a short annealing at 900 C. and air cooling. After this treatment the steel was again subjected at the testing point to an ageing treatment, after which the notching toughness at the testing point was still 10.9 mkgs./cm.

notching toughness was still 9.8 mkgs./cm.". This represents, as compared with the notching toughness of the shaft in completely annealed condition of 10.5 mkgs./cm. a reduction of the notching toughness through ageing of only 6.7%.

A treatment, such as indicated above, as effective against brittleness due to ageing and blue fracture was hithei'to regarded as defective or at least unsuitable on account of the possible deterioration through recrystallization. A publication by A. Pomp, (member of the Institut fiir Eisenforschung at Dusseldorf, Germany), reads as follows:

It must further be noted that in an otherwise sound material a strong reduction of the yield point can be caused by improper treatment, for instance with soft ingot steel, when after slight deformations annealing temperatures between 600 and 900 C. are employed. Such improper treatment results at the same time in astrong coarsening of the structure and consequently a considerable increase in brittleness. It therefore cannot be emphasized sufiiciently to carefully anneal parts which have been deformed, namely at temperatures higher than the A point.

Although the reference to the possible deterioration of the steel through coarsening of the structure is correct, it has been shown nevertheless that careful annealing above the A point is not generally to be preferred, but that actually a very restricted and limited annealing treatment of the steel, either above or below the A point, oifers the possibility, after a previous cold deformation, of obtaining a very considerable increase in quality of the material.

What I-claim, is

1. A process of treating soft ingot low carbon steel to greatly reduce the tendency to blue fracture and brittleness due to ageing which consists in subjecting the steel to a uniform cold stressing to cause a crystallographic direction efi'ect; subjecting the material to a short annealing at 850 C. to 900 (1.; and then air cooling the annealed product; whereby the toughness lost through the cold deformation is reestablished by the annealing while the crystal arrangement caused by the cold deformation is maintained, the reduced tendency to blue fracture and brittleness due to aging being therefore also maintained.

2. A process of treating low carbon steel to render it resistant to ageing which consists in subjecting the steel to a cold working operation and thereafter annealing it at a temperature slightly above the upper critical point thereof, followed by air-cooling.

In testimony whereof I have hereunto set my hand.

HANS MEYER.

CERTIFICATE OF CORRECTION.

Patent No. 1, 843,456. v Granted February 2, 1932, to

' HANS MEYER. I

It ishereby certifiedthat error appears in the above numbered patent requiring correction as follows: In the heading to the printed specification, date of filing application in Germany, for "December 6, 1927" read December 6, 1926; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 5th day of April, A. D. 1932.

M. J. Moore,

'(Seal) Acting Commissioner of Patents. 

